Dataset Information

C9ORF72 repeat expansion in clinical and neuropathologic frontotemporal dementia cohorts.

ABSTRACT:

Objective

To determine the frequency of a hexanucleotide repeat expansion in C9ORF72, a gene of unknown function implicated in frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS), in Australian FTD patient cohorts and to examine the clinical and neuropathologic phenotypes associated with this expansion.

Methods

We examined a clinically ascertained FTD cohort (n = 89) and a neuropathologically ascertained cohort of frontotemporal lobar degeneration cases with TDP-43 pathology (FTLD-TDP) (n = 22) for the C9ORF72 hexanucleotide repeat expansion using a repeat primed PCR assay. All expansion-positive patients were genotyped for rs3849942, a surrogate marker for the chromosome 9p21 risk haplotype previously associated with FTD and ALS.

Results

The C9ORF72 repeat expansion was detected in 10% of patients in the clinically diagnosed cohort, rising to 29% in those with a positive family history of early-onset dementia or ALS. The prevalence of psychotic features was significantly higher in expansion-positive cases (56% vs 14%). In the pathology cohort, 41% of TDP-43-positive cases harbored the repeat expansion, and all exhibited type B pathology. One of the 17 expansion-positive probands was homozygous for the "nonrisk" G allele of rs3849942.

Conclusions

The C9ORF72 repeat expansion is a relatively common cause of FTD in Australian populations, and is especially common in those with FTD-ALS, psychotic features, and a strong family history. Detection of a repeat expansion on the 9p21 putative "nonrisk" haplotype suggests that not all mutation carriers are necessarily descended from a common founder and indicates that the expansion may have occurred on multiple haplotype backgrounds.

SUBMITTER: Dobson-Stone C

PROVIDER: S-EPMC3430710 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Variants in transmembrane protein 106 B (TMEM106B) modify the disease penetrance of frontotemporal dementia (FTD) in carriers of progranulin (GRN) mutations. We investigated whether TMEM106B is also a genetic modifier of disease in carriers of chromosome 9 open reading frame 72 (C9ORF72) expansions. We assessed the genotype of 325 C9ORF72 expansion carriers (cohort 1), 586 FTD patients lacking C9ORF72 expansions [with or without motor neuron disease (MND); cohort 2], and a total of 1,302 controls for TMEM106B variants (rs3173615 and rs1990622) using MassArray iPLEX and Taqman genotyping assays. For our primary analysis, we focused on functional variant rs3173615, and employed a recessive genotypic model. In cohort 1, patients with C9ORF72 expansions showed a significantly reduced frequency of carriers homozygous for the minor allele as compared to controls [11.9 vs. 19.1 %, odds ratio (OR) 0.57, p = 0.014; same direction as carriers of GRN mutations]. The strongest evidence was provided by FTD patients (OR 0.33, p = 0.009) followed by FTD/MND patients (OR 0.38, p = 0.017), whereas no significant difference was observed in MND patients (OR 0.85, p = 0.55). In cohort 2, the frequency of carriers homozygous for the minor allele was not significantly reduced in patients as compared to controls (OR 0.77, p = 0.079); however, a significant reduction was observed when focusing on those patients with frontotemporal lobar degeneration and TAR DNA-binding protein 43 inclusions (FTLD-TDP; OR 0.26, p < 0.001). Our study identifies TMEM106B as the first genetic factor modifying disease presentation in C9ORF72 expansion carriers. Homozygosity for the minor allele protects carriers from developing FTD, but not from developing MND; similar effects are seen in FTLD-TDP patients with yet unknown genetic causes. These new findings show that the protective effects of TMEM106B are not confined to carriers of GRN mutations and might be relevant for prognostic testing, and as a promising therapeutic target for the entire spectrum of FTLD-TDP.

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